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Physics questions on badminton

Hello, I have come up with 3 physics question on badminton to improve my backhand clear and attacking lift.

1. Does a good smash have a high spinning rate, low or no spinning?
A good smash = fundamental smash pose used(to endure your wrist, elbow, and shoulder) + high average speed generated

2. Will a spining (revolution) shuttlecock drop shorter or farther in horizontal distance than a no-spinning shuttlecock?
One of coaching vids said spin will cause a shuttlecock to travel farther, but I heard a spinning golf ball cause to lift and to fall short in horizontal distance.

3. Will Smashing a spinning shuttlecock result a faster average speed of shuttlecock? Assume that smash cause a shuttlecock to stop spinning. (I am not sure that that assumption is realistick...)- this question is related to question no.1.

I am not here to exam you, but just want to know physics behind badminton.
Thank you for your time.

1. what is your definition of "good smash"? do you mean placement, angle, or power, or a combination of the three?

2. shuttles spin differently than any other kinds of "balls" because shuttles are not spherical. even golf balls have top spin, back spin, and side spins that can make the ball travel further or hang shorter. however, i wonder where you heard this video because generally spins/slicing make the shuttle drop faster because ur not making a full contact with the racquet but only brushing the shuttle which has less force.

3. in order to do a smash, your opponent must've cleared to you... and I have never encountered a badminton clear shot that adds spin on it. a slicing drop shot adds spin, but in order to clear deep, i think you need to make a clean contact with the shuttle

1. The higher the smash speed the faster the spin. As the shuttlecock slows down, so does the spin.
2. A golf ball is round. A shuttlecock isn't. Different rules apply.
3. No.

Also, a lift is a defensive shot. I've yet to see an attacking lift.
The physics of a clear or smash, whether backhand or forehand, is not about the shuttlecock or how it spins. It's about how much Force(F) you're able to transfer to the shuttlecock. And F=ma.

if you watch a shuttlecock dropped vertically from very high, you will notice that it will naturally spin. which is not surprising as the shuttlecock looks some what similar to a fan/propeller shape.

given that, it is not hard to see that the least resistant path to a shuttlecock travelling through air is one that is spinning.

the question is how fast?

well, if you drop it, you will find that the rotational speed when it reaches terminal velocity is not very fast.

so for a shuttlecock at smash speed will need to spin much faster to reach its optimal spin to travel through air with least resistance.

however, what happens if the shuttlecock spins faster or slower than its optimal rotational speed? then the shuttle slows down due to too much air resistance produced by the spin. this is how a player can control the trajectory for the shuttle during a overhead drop shot to make it curve and hugs the net.

2. A high spin rate smash will drop shorter as you are artificially increasing the air resistance.

3. The shuttle will always be spinning, but a faster spinning shuttle will be slowing faster than a normal spin shuttle. So my explanation would be similar to a trampoline, a person dropping onto the trampoline from 10m would have a greater speed on impact and result in a higher bounce (faster smash); dropping from 2m would create less rebound and a slower smash. So a slower spinning shuttle should be travelling faster and aid the smash speed.

It is all about air turbulence/resistance

Originally Posted by fmqpt791004

Hello, I have come up with 3 physics question on badminton to improve my backhand clear and attacking lift.

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Reading into your questions, I believe that you are thinking that a vigourously spinning shuttlecock will travel faster and further than one which is spinning less. I afraid to tell you that it is the opposite. It is all about the air turbulence/resistance.

Originally Posted by fmqpt791004

1. Does a good smash have a high spinning rate, low or no spinning?
A good smash = fundamental smash pose used(to endure your wrist, elbow, and shoulder) + high average speed generated.

Here, I think you are just talking about the fast flying speed of a shuttlecock.

Answer: The more the rotation/spinning of the feathers of a shuttlecock, the more the air resistance is added to its flight. Therefore, the answer is - The shuttlecock will travel faster when it has less spin.

Originally Posted by fmqpt791004

2. Will a spinning (revolution) shuttlecock drop shorter or farther in horizontal distance than a no-spinning shuttlecock?

Answer: It is answered in the Question-and-Answer in 1.

Originally Posted by fmqpt791004

3. Will Smashing a spinning shuttlecock result a faster average speed of shuttlecock?

Answer: If you could add more spin (in the same direction of original spin), then the shuttlecock will fly slower. Same explanation as answered in Question-and-Answer in 1.

BTW, because of the way the feathers are over-lapping, with a clockwise spin (travelling from you) of shuttlecock, it will fly faster than when it is with an anti-clockwise spin. This is because of more air turbulence/resistance in the anti-clockwise spin; hence the shuttlecock will travel slower.

If you have a propellor which was powering a plane moving through the air, and then you turn the engine off but keep the plane moving at constant velocity, the propellor will slow down, but while its slowing to the "natural" velocity it will still power the plane.

So I would think that if the shuttle is spinning for a "faster" speed that it should in the forwards direction then the rotational energy of the spin will be converted to propel the shuttle forwards, i.e. the shuttle slows down LESS than if it was at the "correct" speed.

To put it another way, if you have a shuttle spinning on a lathe, then the feathers will blow air either forwards or backwards depending on the direction of the spin. So if the spin produces an airflow of 100kph backwards, then that is the "natural" spinning speed of a shuttle travelling at 100kph forwards. Now if the shuttle feather rotation was making a 150kph wind backwards while the shuttle itself is travelling at 100kph forwards, then the shuttle is effectively blowing a 50kph wind backwards, which would make it go forwards faster.

......if you have a shuttle spinning on a lathe, then the feathers will blow air either forwards or backwards depending on the direction of the spin.

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If what you've said is true, then all coaches would train beginners to hit the shuttlecock with as much spin as possible (to power up the shuttlecock's flight distance). I am a qualified coach for decades (and is still open to new ides), but I have never heard that a spinning shuttlecock will travel faster and/or go further.

However, most of us know that the more slicing action we put on a smash, the shuttlecock would dip and slow down earlier/quicker.

If you have a propellor which was powering a plane moving through the air, and then you turn the engine off but keep the plane moving at constant velocity, the propellor will slow down, but while its slowing to the "natural" velocity it will still power the plane.

This analogy is a bit misleading. The only thing acting on it after it leaves the string bed is air resistance. This is the same with a plane after the propellers are turned off. Needless to say, putting more spin on it will create more air resistance. In the case of the shuttlecock feathers, they block more area than an plane propeller as the spin is not powered after the initial hit. In addition, the angle of the shuttle feathers are not the same as a propeller, so they don't necessarily blow any air backwards or forwards.

A plane only slows down relatively less because of its mass, but it will slow down to zero nonetheless if the propellers are not working.

This analogy is a bit misleading. The only thing acting on it after it leaves the string bed is air resistance. This is the same with a plane after the propellers are turned off. Needless to say, putting more spin on it will create more air resistance. In the case of the shuttlecock feathers, they block more area than an plane propeller as the spin is not powered after the initial hit. In addition, the angle of the shuttle feathers are not the same as a propeller, so they don't necessarily blow any air backwards or forwards.

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Yes, I think so too; that NanoBatien thinks that the feathers rotation will propel the shuttlecock forward.

We can also consider this - If a clockwise rotation of the feathers can propel the shuttlecock forward, then wouldn't a anti-clockwise rotation propel it backward? Here, I am thinking of the propeller of the motor of a boat (where the propeller can drive the boat forward or backward).

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If what you've said is true, then all coaches would train beginners to hit the shuttlecock with as much spin as possible (to power up the shuttlecock's flight distance).

Just because the spin helps propel the shuttle forward doesnt necessarily mean that slicing the shuttle is more efficient than just hitting the shuttle dead on.

Maybe the normal slicing action is the one which puts reverse-rotation on the shuttle. The flightpaths resulting from the two slicing directions dont really seem the same to me, which is consistent with the direction of rotation affecting the flight path.

Originally Posted by chris-ccc

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We can also consider this - If a clockwise rotation of the feathers can propel the shuttlecock forward, then wouldn't a anti-clockwise rotation propel it backward? Here, I am thinking of the propeller of the motor of a boat (where the propeller can drive the boat forward or backward).

You are right that I think that the reverse rotation of the shuttle will propell it backwards, in that it will exert an additional backwards force on the shuttle. But since the shuttle is moving forwards very fast, the reverse rotation only slows down the shuttle.

Originally Posted by hybriddragon

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Needless to say, putting more spin on it will create more air resistance.

I do not understand what you mean by "needless to say". It does not seem obvious to me that putting more spin on an object will make it create more air resistance. For example, if you put more spin on a plane propellor, you are not creating more total air resistance, quite the opposite in fact.

To use my analogy on a plane, when you run the propellors, the propellors are blowing air backwards at 150kph, and the plane is going forwards at 100kph. Now the moment you turn the engine off the propellor speed doesnt not change instantaneously, so the propellor is still propelling the plane. Then of course the propellor will slow, and it will slow until its turning at the speed of the plane.

I do not understand what you mean by "needless to say". It does not seem obvious to me that putting more spin on an object will make it create more air resistance. For example, if you put more spin on a plane propellor, you are not creating more total air resistance, quite the opposite in fact.

To use my analogy on a plane, when you run the propellors, the propellors are blowing air backwards at 150kph, and the plane is going forwards at 100kph. Now the moment you turn the engine off the propellor speed doesnt not change instantaneously, so the propellor is still propelling the plane. Then of course the propellor will slow, and it will slow until its turning at the speed of the plane.

I am not saying it's obvious, that was just a connecting phrase. I'm sorry if it offended you in some way.

Anyhow, I will attempt to clarify your misconception of why your analogy doesn't work. There two critical differences you must understand between propellers and shuttlecocks.

First critical difference:

If you view the attached image on which I have crudely drawn at the bottom of my post, you will see that propellers cut through air differently than shuttlecocks. On the left side of my horrible drawing is the shape as seen from the front of the object. As you can see on the right side, the fundamental difference is that propellers cuts through air like a screw (similar to a screw going into wood) and that's how it propels the objects it is attached to forward in the horizontal direction. The drawing on the right side shows how the each object cuts through the air as it moves forwards in the x direction (horizontal)

In the case of the shuttlecock, it is more of a shape of a cone. As it cuts through air, it leaves a trail, as shown in my ugly drawing. This is because most of the air does not pass through the feathers. The surface area and the angle of the feathers deflect the air in an outward direction which actually slows the bird down. Spinning the shuttle more only acts to create more air turbulence around the feathers to deflect air around the shuttlecock.

Second critical difference:

Combustion powers the engine which powers the propellers. The plane attached to propellers accelerates forwards in the horizontal direction only when it is powered. Otherwise, it will decelerate to zero eventually from the speed the propeller got it to. (This is because of the air resistance on the plane.) Remember, propellers serve to only accelerate the plane to a certain speed only when powered (or spinning). When it is not powered, air resistance acts on the plane to slow it down to zero horizontal velocity eventually. (I must point out that I never said that the plane would slow to zero instantaneously.)

A shuttlecock's spin is not powered throughout the flight. The only force imparted on it is the initial impact from the string-bed of the racket. Afterwards, only air resistance is acting upon it. The shuttle spins not because it is creating any force of any kind, but rather because the shape of shuttle causes it to turn as it cuts through air.

Putting it all together:

Putting both things together, we can conclude that because of the shape of the shuttle, the spin does not necessarily induce a higher speed the same way a propeller does. This is mainly because of the way the shuttle cuts through the air as opposed to how a propeller cuts through the air. Because they do not cut through the air the same, the effects of spinning a propeller and a shuttle are not the same. Therefore, the analogy of comparing the effects of propellers on planes with shuttlecocks is not an accurate representation of what actually happens.

In a final note, I'd like to point out that air resistance and how air moves around an object depends heavily on the shape of the object. Different shapes will cause different effects when moving through air.

If there is anything unclear about my explanation, just ask.
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I personally think that spin has a very marginal effect on the speed of the shuttle. The power of the impact and the racket face (i.e. slicing v.s. hit directly) has more relevance to speed of the shuttle than its spin. If you were to have a shuttle at a certain velocity, spinning faster or slower, the difference it makes is too small to matter. I believe chris-ccc's explanation was quite accurate as to how spin affects the shuttle velocity.

However, if you were to ask if spin affects flight path, then it might be a different story.

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Another thing to ponder about: If we assume an opposite-spinning shuttle is slower, does this mean most of the shots left-handers hit are slower? If Lin Dan was right handed, would his smashes be quicker?

Spin or rotation of a shuttle is one of four main design parameters in a badminton feather shuttlecock.
The very best feather shuttlecocks spin or rotate on their axis much faster than cheaper ones and many times faster than plastic shuttlecocks.

I don't want to get into any arguments at great lengths about this. But take it from me, the fastest spin rate is when you smash a shuttlecock and the slowest in a natural state is when it is in precession-that is when it gyrates at height when you hit a very high shot and it turns over to descend vertically. Great net players 'spin' (actually knocking the shuttle off its natural spin intentionally) to reduce its spin to slow motion spin thus rendering it unplayable.
Think of a spinning top, the faster the top spins the more stable/straight it is. Then give it a knock like the way great net badminton players do a net net tumble, then the top's or shuttle's spin almost disappears and the game stops.

To repeat, all shuttlecocks must spin because they are part of the design and the spin rate gets worse with wear and tear which then requires a shuttle change. Now, you know why a new shuttle is always faster than one that has gone through a few rallies.

hybriddragon do you have any formal qualifications or some special knowledge about aerodynamics? If not this might be a case of the blind leading the blind and we should just give up.

Axial spin only marginally affects the speed. But it is still an interesting question.

I think your depiction of propellor airflow is wrong. A correctly designed propellor will actually give quite a uniform airflow. For example a wind turbine's power output is primarily determined by the swept area of the blades.

Having said that, a propellor airflow is more Bernoulli type, while a shuttlecock airflow is more of the wind hitting flat area type. So maybe we cannot treat them the same.

Now of course much of the air is going around the sides of the cone shuttle, but it is the air thats going between and next to the feathers thats causing the tiny increase/decrease in shuttle speed that we are interested in. So we cannot just ignore that tiny airflow.

Suggesting that a spinning shuttle creates more turbulence is an interesting one, but it is not obvious to me that a spinning shuttle is necessarily more turbulent, nor is it obvious that the turbulence generated negatively affects the shuttle speed.

A left hander and righthander perfect square on hit is of course the same speed. But slices of the shuttle (standard and reverse) would have different effects.

hybriddragon do you have any formal qualifications or some special knowledge about aerodynamics? If not this might be a case of the blind leading the blind and we should just give up.

I must say that my problem lies with your analogy. I do not claim to be an expert, but I know enough about air resistance/flow to see your analogy doesn't really add up. Nothing you have said seemed to have convince me that your analogy is correct.

In the case of discussion of shuttlecock aerodynamics, we might as well all give up. As a badminton community, I think the best we can do to answer the opening post is just use our experience with badminton as inference. We all have our different backgrounds. If we're looking for scientific qualifications to discuss questions such as this, we might as well not discuss anything at all. I'm not sure there are any experts in the aerodynamics of a shuttlecock in this forum, unless you happen to work for R&D for Yonex and have done extensive controlled testing on shuttlecock flight.

As for propellers, internet is my knowledge. I don't have any special qualifications other than my Newtonian physics classes in college. I didn't have any extra prior knowledge, but after looking at several sites explaining how propellers work, I've gotten the gist of it. What qualifications do you have? You seem well versed enough to whip out the fact that airflow for a propeller is a 'Bernoulli' type. I understand Bernoulli principles when it comes to probability, but what does it mean in terms of aerodynamics?

I think your depiction of propellor airflow is wrong. A correctly designed propellor will actually give quite a uniform airflow. For example a wind turbine's power output is primarily determined by the swept area of the blades.

Of course, my drawing is not to scale and was created in 5 minutes. I drew it to convey the basic idea that propellers go through air like a screw. A shuttlecock does not produce the same effect. As you have said, we cannot treat them the same, so why do we make analogies between them?

Now of course much of the air is going around the sides of the cone shuttle, but it is the air thats going between and next to the feathers thats causing the tiny increase/decrease in shuttle speed that we are interested in. So we cannot just ignore that tiny airflow.

I don't suggest we ignore it completely, but it obviously isn't the biggest factor that produces the biggest gains for a smash. (Which is what the opening question was for- a smash) If we think in terms of gains, what happens when we double the revolutions of a shuttlecock. What percentage of gain in velocity do get? (Keeping all other factors constant) I have a feeling we don't even get a 1% increase in speed. Of course, this question cannot be answered without a proper experiment. (Controlling for other factors)

If I were to think of a physics of producing a strong smash, a shuttlecock's spin is certainly not the first thing I would think of.

Maybe we should write a letter to Yonex to see if they'd like to enlighten us on the physics of a shuttlecock.

I don't suggest we ignore it completely, but it obviously isn't the biggest factor that produces the biggest gains for a smash. (Which is what the opening question was for- a smash) If we think in terms of gains, what happens when we double the revolutions of a shuttlecock. What percentage of gain in velocity do get? (Keeping all other factors constant) I have a feeling we don't even get a 1% increase in speed. Of course, this question cannot be answered without a proper experiment. (Controlling for other factors).

If I were to think of a physics of producing a strong smash, a shuttlecock's spin is certainly not the first thing I would think of.

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Throughout my many decades of doing professional coaching, I have tested and found that when smashing with a slicing action (therefore generating more spin), the forward velocity will decrease. The comments were made in Posts #7 and #9.

Originally Posted by chris-ccc

The more the rotation/spinning of the feathers of a shuttlecock, the more the air resistance is added to its flight. Therefore, the answer is - The shuttlecock will travel faster when it has less spin.

and, if the shuttlecock will travel faster when it has more spin;

Originally Posted by chris-ccc

then all coaches would train beginners to hit the shuttlecock with as much spin as possible (to power up the shuttlecock's flight distance).

This is especially true for beginners who could not hit their 'Clears' from one end of the court to the other end (in other words, the full distance of 44 feet).
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